Tor Browser is a Firefox ESR(extended support release) tweaked in a way that are supposed to improve your security and anonymity. Because it's a long-term supported release - it's obvious that it's not the latest one, but security patches are supposed to be merged into it with the same speed as in a mainline one. Tor Browser does it's job well, but it's still a browser, so it's unable to protect you as wide as an isolated VM